1. Filed of the Invention
The present invention relates to a method and apparatus to determine the theoretical yield of the coal and minerals concentrate at different impurity levels. More particularly, the invention relates to a method and a float-sink apparatus adaptable to determine beneficiation prospects of coal, metallic, non-metallic ore and, industrial minerals in a beneficiation process.
2. Description of the Related Art
In case of coal or any other mineral, beneficiation prospect of the feed is evaluated by graphically developing a curve which indicates theoretical yield values of the concentrate at different impurities level. The theoretical yield values are considered as the maximum achievable yield at the corresponding impurities level in the concentrate. This is a valuable information as it directly shows the liberation status of the feed, concentrate yield versus grade relation and loss of values in the reject. The theoretical yield values are compared with the actual yield values of the plant or machine to arrive at the efficiency of the plant or the machine. The general expression for the efficiency is =[−(Actual yield)/Theoretical Yield)]*100.
Theoretical yield for coal is determined through a series of float-sink tests. The process starts with the preparation of heavy media liquids of specific gravity 1.3 to 2.2 with intervals of 0.1. These liquids are prepared by mixing benzene, tetrachloro-ethylene and, bromoform in different proportions. The float-sink tests are conducted with feed coal at size ranges identical to the size ranges fed in the washery. The coal is first tested on 1.3 specific gravity liquid and the float obtained is the purest coal in the feed. The sink is again treated on the next higher specific gravity liquid which is 1.4. The process continues till float and sink fractions are obtained from 2.2 specific gravity liquid. At the end of the process along with one sink fraction, float fractions from each specific gravity liquids are generated. All these fractions are then analysed for their ash content. Ash content of the float from 1.3 specific gravity liquid is minimum which increases successively for the rest of the float fractions and the lone sink fraction shows the highest ash content. This trend is universal for coal as the specific gravity of ash containing minerals is higher than pure coal matter. These set of data is used to generate the theoretical yield-ash curve of washed (clean) coal and is often described as the washability curve. Although in case of coal the process described hereinabove is well established, however in case of minerals such process is not that established as the liquids used for float-sink tests of coal cannot be used in minerals as the specific gravity of minerals are much higher than that of coal. In case of minerals, the application of float-sink tests is industry specific and often not conclusive by itself. For example, the known beneficiation methods followed in beach sand minerals involves testing of the feed in bromoform (a liquid of specific gravity 2.88). The liquid separates all heavy minerals from the silicates. The heavy minerals are then washed with acetylene prior to semi quantitative estimation of minerals through microscopical method.
In iron ore industry two different types of methods are being used, but none of them is self sufficient. In the first method, the atomised Ferro-silicon is mixed in different proportions with water to create suspended solutions of solid which could provide mixtures of different specific gravity. Thereafter, the feed iron ore is tested in the mixtures having low to high specific gravity. The float fractions and the lone sink fraction are then chemically analysed for their iron content. In case of minerals float fraction contains more of impurities and the sink represents the purest form of minerals. The known method is not self sufficient because of the difficulties in preparation of high specific gravity medium through this prior art method. Therefore, this known method fails to allow extension of the theoretical yield-grade curve to a desired grade concentrate level.
In the second method, three separate specific gravity liquids namely; ethylene bromide, di-iodomethane and clarici solution of specific gravity 2.96, 3.30 and 4.03 respectively, are used in a sequence. These liquids are immiscible to one another and thus, liquids of intermediate specific gravity cannot be generated by mixing which remains the major disadvantages of this known method. The second method generates a few discrete theoretical yield values corresponding to concentrate grade, instead of a continuous curve and thereby the purpose of the tests is often partly defeated. Furthermore, a liquid of specific gravity higher than 4.03 is often required to separate iron concentrate of desired grade from a poorly liberated ore. In such cases, the theoretical yield of the concentrate cannot be obtained from this test. In addition, the float-sink analysis is carried out with organic liquids which are not environment friendly and often hazardous. Most of these liquids are costly and not readily available in the market. Owing to these disadvantages, the float-sink tests are not a regular practice in mineral sector resulting to either yield loss or deterioration of the concentrate quality in the plant.